A researcher discovered that people who have low levels of immune-system activity tend to score much lower on tests of mental health than do people with normal or high immune-system activity.The researcher concluded from this experiment that the immune system protects against mental illness as well as against physical disease.
The researcher's conclusion depends on which of the following assumptions?
因为人有mental illness的时候他的immune system activity是low的。所以当题干结论是高的immune system activity can protect against mental illness,也就是说low 的immune system activity不能protect people从而很容易有mental illness.
所以答案说mental illness 不会导致immune system activity降低是为了排除这个因素:是mental illness 先存在而导致了immune system activity降低,而不是因为immune system activity降低所以导致了mental illness.